Hypodermic syringes have been used in medicine for countless years. They find use for the injection of fluids into the body and for the removal of sample fluids from the body. Most syringes have a common business end in the form of a sharp needle. For as long as syringes have been used, countless medical workers have been accidently picked by an exposed needle. An accidental pricking causes little harm if and only if the needle has not been contaminated by being inserted into a body otherwise the needle would still be sterile (i.e. no germs, no bacteria, no virus, etc. will be present on the needle). The major concern occurs if the accidental pricking of the medical worker occurs after the needle has been inserted into a body. Today's major dread is exposure to HIV, although exposure to Hepatitis B should not be overlooked.
There have been many efforts by previous medical workers to devise a safe and certain method for sheathing a needle after its use and before the syringe has been properly disposed. These methods or inventions have taken two avenues:
1) an external sliding sheath that covers the needle, and
2) a system to retract the needle into the body of the syringe.
The simplest devices have been those that externally sheath the needle while the most complex have been those that retract the used needle. All of these safety devices must have a positive locking device to either keep the guard (or sheath) in place or keep the retracted needle in place within the body of the syringe.
Generally the sheathing devices use an external catch or tab molded onto the outside of the syringe body. This results in a distortion of the circular shape of the syringe and makes it almost impossible to insert into another instrument, such as a Blood Gas Analysis Machine, so the body sample contained within the syringe can be safely and hygienically injected into that instrument. Generally speaking, in these externally guarded syringes the sheath must be withdrawn to allow re-injection of the sample; thus the worker is again exposed to a prickly potential.
The devices which use a retractable needle generally accomplish their purpose by using a loaded spring and latches within the syringe. Thus after the syringe is used, the plunger is pushed harder or a latch is pressed and the needle "shoots" back inside the syringe body. This technique appears to work in spite of the number of parts and the potential for an unwanted retraction. Unfortunately if these devices were to be used for Blood Gas Analysis or any analysis that requires the taking of a body sample for re-injection into a machine, the retracted needle will interfere with the release of the sample. That is, with the needle firmly wedged inside the body of the syringe, the plunger cannot move back into the body of the syringe and force the sample out of the syringe.
An object of this invention is to make available a safety syringe in which the needle can be retracted into the body of the syringe after use and yet not interfere with the operation of the syringe when it is used to collect body samples; yet be capable of regular use. Another object of the invention was to provide a syringe that was easy to manufacture and did not use a loaded spring to retract the needle; thus making accidental retraction impossible. Furthermore, the syringe becomes perfectly safe after needle retraction and cannot accidently prick a worker in the laboratory when a body sample is being injected into an analysis machine. In addition, by using a retractable needle, the syringe retains its standard circular shape and will fit into any of the standard laboratory analysis machines. Finally, because the actual needle retracts out of the way, "the nipple" of the syringe is safely available for attachment to analysis machines--this is the preferred method of attachment to such machines.